I have a Contacts folder. The XP machine it came from won't run.  I copied the Contacts folder to a USB flash using Linux.

So I have all the contacts in this folder.  But I can't copy them to the contacts folder in the Win10 machine and I can't import them because they aren't any format that Thunderbird recognizes.  I can't make them CSV files or anything else that I've tried.

Somehow I got one folder open and tried to export them as CSV but no file was created.  Tried several times.

I really hate to have the guy lose all his contacts.  But I know I can't get the old computer to run long enough to export the address book.  So all I can do is copy the folder that holds the files.

I've never encountered this problem, I've always been able to export address books.